The method of detecting standing bowling pins in use in most commercial bowling establishments comprises mechanical switches or microswitches disposed on the pinsetter of a bowling machine which faces the predetermined positions of the ten pins. A certain time after the first ball is thrown, the pin setter is brought down to pick up the remaining pins. The presence and locations of the remaining pins is electromechanically signaled by the microswitches. The output signal from each of the switches is applied to an indicating lamp, and a count of the energized switches takes place to provide a pinfall count. However, this system suffers from both a slow operating speed and a tendency to jam.
A number of efforts have been made to eliminate mechanical pinsensors by replacing them with electro-optical bowling pin sensing devices. These detecting systems could not be placed overhead above the pins in a plane field of view, because the pinsetting apparatus occupies this space. The detection system could not be in the kickback wall on either side of the pin locations, because of the danger of damage to the optics by the bouncing pins. The optics could not be directly in front of the pin placements because of the necessity of maintaining a clear field of view of the pins from the front of the alley. All these restrictions combine to require that the detection portion of the electro-optical system view the pins from an angle wherein the pins are partially obscured behind one another in angled rows.
In several known systems light zoning techniques were utilized wherein the bowling pins are illuminated in a given time sequence. Photo-sensors are associated with each pin and are activated so that as each bowling pin is illuminated, that detector is synchronously interrogated to determine if the associated pin is standing. The result of such a system is that when a pin is displaced from its set position to a position which is adjacent to another pin, the light reflected from this moved pin and the unmoved pin will be detected by the same photocell and the two will be counted as a single pin. This presents the dual problem that an erroneous pin count will be made, and that an inaccurate representation of the actual standing pins will also result. Error also results when a pin moves to lie partially within two zones and is counted twice, again providing an inaccurate pin count and pin location map.
An effort to overcome these deficiencies is disclosed in Logemann et al, U.S. Pat. No. 3,847,394 which uses a plurality of television cameras mounted at angles in front of the bowling pin standing area to scan the standing area. The image on the TV camera screen is then scanned by a scanning beam to break the camera image down into minute segments. An effort is then made to assign each detected pin image to a preestablished pin identifying region. It is claimed that where pins move to present overlapping images, that a correct pin count is achieved; however, since the TV cameras are dealing with just a two-dimensional view of the pin field without any analysis of the depth of field, where a pin does move there can be no way of assigning that pin to its actual location. A further difficulty with this system resides in the use of the TV cameras which results in an expensive system to mount on a plurality of bowling alleys.
Only one known effort has been made in the past to use acoustic transducers which are much more impervious to physical damage from pinfall than electro-optic systems for detecting pin count and pin location. This system, disclosed in Eisenberg, U.S. Pat. No. 3,099,447 comprises inserting transducers in the alley under each pin spot. The electrical system for the transducer comprises a bridge circuit having an operating frequency set to the fundamental resonance of the transducer. The bridge is balanced in the absence of a standing pin; if a pin falls, the bridge becomes unbalanced and provides a signal to an indicating means. Thus, an indication of a standing or fallen state may be developed for each pin. However, this system of mounting transducers in the bowling alley, since it requires reconstruction of the most important portion of the bowling alley, is also quite expensive to install. Further, the embedded transducers are not able to differentiate between a pin which slides away from its assigned spot, and one which has fallen.